1. Field of the Invention
The present invention relates generally to the field of presbyopic vision correction and, more particularly, to the use of a wavefront sensor for the measurement, design, fit and dispensing of a vision altering optic or vision correcting procedure to improve presbyopic correction and visual performance.
2. Description of Related Art
A form of age-dependent vision deterioration experienced sooner or later by 100% of the population is called presbyopia, i.e., the inability to accommodate or focus on objects close to the eye. Two well-known methods for dealing with presbyopia include alternating vision style correction and simultaneous vision style correction.
In an example of an alternating vision style correction, two (or more/multi-focal) distinct optical regions of a translating style contact lens are designed, one optimized for distance vision and the other for near vision. Typically in an alternating vision bifocal contact lens, the lens will translate on the eye such that the pupil is mostly covered by the distance viewing portion of the lens; however, when eye gaze points downward, such as when a person reads a newspaper, the lens translates on the eye such that the pupil is mostly covered by the near distance viewing portion of the lens.
Alternatively, simultaneous style vision correction has been provided through, e.g., contact lenses, IOLs, refractive surgery, etc. In this style of correction, all light from the object goes through the pupil at the same time, preferably with a 50/50 split between near distance and far distance object light. Any one of a number of refractive or diffractive bifocal or multifocal designs are used to focus light from objects ranging in the field of view from far distance (greater than about 7 m) to near distance (as close as about 0.25 m but typically about 40 cm) on the retina at the same time.
As a person gets older, not only do they lose the ability to accommodate, they also experience an increase in what are known as higher order wavefront aberrations. These include, but are not limited to, spherical aberration, coma, irregular astigmatisms (e.g. triangular astigmatism or trefoil), and others. The aberrations corrected by spectacles or single vision contact lenses are limited to defocus and astigmatism which are generally referred to as lower-order aberrations. An increase in spherical aberration brought about, for example, by advancing age, will decrease nighttime vision quality. This may manifest itself as halos or glare around headlights or other light sources. Unfortunately, for the presbyope hoping for better near distance vision with a translating-style contact lens, the correction of the spherical aberration for improved far distance, night time vision results in a decrease in near vision depth of field; i.e., the amount an object's distance can be shifted before the retinal image of the object has too much blur.
There are also vision tradeoffs for the multifocal, simultaneous style correction lens wearer. Although there are claims of excellent clinical success with a number of simultaneous vision bifocal and multifocal designs, actual published success rates with refractive and diffractive contact lenses for presbyopic correction range only from about 20% to 50% of the general presbyopic population. One of the apparent limiting factors of all current simultaneous style vision correction for presbyopia is lens misalignment; i.e., the lack of control of the centration of the lens relative to the optical axis of the patient. Unfortunately, the induced aberrations caused by the optical misalignment of the eye with the simultaneous vision correction lens reduces visual performance to the point that vision quality is unacceptable to the patient at any viewing distance.
One approach to alleviating vision performance problems is, presumably, to eliminate all optical aberrations in the eye. In the first instance, this solution may not be technically feasible, although correction of wavefront errors via customized refractive surgical techniques and/or customized contact lenses, inlays, onlays, and IOLs, for example, is becoming better understood each day. Moreover, the elimination of all optical aberrations in the eye may not be desirable. For example, reducing spherical aberration will adversely affect depth of field, as discussed above, thus some residual spherical aberration may be desirable for optimum vision quality.
Accordingly, there is a need for vision correcting methods and devices that address the aforementioned problems. In particular, methods and apparatus are needed for providing multifocal lens correction of presbyopia with improvement, or at least no degradation, of other aspects of vision quality.